The present invention relates to a light-diffusing film having pores for use in a backlight unit of a TFT-LCD (Thin Film Transistor-Liquid Crystal Display), and more particularly, to a light-diffusing film, in which pores are formed in a light-diffusing layer laminated on one surface of a base sheet, thereby increasing total light transmittance and light diffusibility.
In general, LCDs can be manufactured to be small and ultra slim, and can realize low power consumption and high image quality, and thus are receiving attention for use as various mobile image display devices or stationary image display devices. However, in the display using liquid crystals, the liquid crystal itself has no emission properties, unlike other flat displays, and an additional emission unit is thus required to increase the brightness of a display screen.
The emission process for the additional emission unit is largely classified into a front-light process and a backlight process. In the front-light process, a light source is attached over the front surface or front lateral surface of the display to illuminate the surface of the display. However, as the size of the display is increased, it is difficult to realize techniques for uniformly diffusing light from the light source over the surface of the display. Further, unlike the backlight process mentioned below, when the light is radiated from the front lateral side, reflective light is generated from the surface of the display, and limitations are imposed on designing the front surface of the display.
Meanwhile, the backlight process is an indirect lighting process for enhancing the brightness of a display screen in a manner such that light originating from the light source of a backlight unit mounted to the back surface of a display device is transferred to the opposite side through a light guide plate and then reflected at a reflective plate, such as a metal deposition plate or an opaque white plate, to allow the light to move forward. Thus, the backlight process is a light emission technique capable of overcoming the problems of the above-mentioned front-light process. In the backlight process, although methods of disposing large numbers of light sources to a backlight unit or of increasing the power of the light source itself have been devised in order to provide clear and bright images, they suffer because the heat generation and power consumption rates of the backlight unit are increased, undesirably reducing the lifetime of products. In particular, in the case of mobile image display devices, operation time may be shortened. Thus, in addition to the additional supply of the light source, another technical means for increasing the light intensity of LCD is required. To this end, the development of a light-diffusing film, which functions to allow light emitted from a light source lamp to pass through a diffusion plate or a light guide plate while being uniformly diffused without loss, has been proposed as a solution appropriate for increasing the light efficiency of a backlight unit. Therefore, thorough research into methods of conferring high total light transmittance and haze to the light-diffusing film is being conducted.
In this regard, Japanese Patent Laid-open Publication No. Hei. 09-270104 discloses a technique for preparing a light-diffusing resin laminate having a resin layer prepared by uniformly dispersing a light-diffusing material in a base resin containing rubber polymer. Japanese Patent Laid-open Publication No. Hei. 11-164649 discloses a light-diffusing film comprising a transparent substrate having a fine roughness on one surface thereof and a light-diffusing layer formed of an ionizing radiation curable resin on the other surface of the transparent substrate. However, such conventional techniques are disadvantageous because limitations are imposed on increasing the light transmittance and light diffusibility of the light-diffusing film, merely by using the light-diffusing material or partially changing the light-diffusing surface.